Consumer Concerns
Escherichia coli O157 (E coli)
Why this note?
There have been a number of media reports on outbreaks of diarrhoeal illnesses caused by the the E.Coli O157 bacteria, including reports from North America involving water supplies. The purpose of this note is to provide reassurance about the safety of public water supplies in England and Wales.
Why the concern?
In contrast to the harmless E.Coli strains normally found in the gut of all warm-blooded animals, the O157 strain produces a potent toxin. This causes severe diarrhoea and in some cases renal failure and death. Toxigenic E.Coli, including O157 and other strains, are carried by 10-15% of healthy ruminants, including cattle, sheep, goats and deer. The bacteria may be transmitted to humans by consumption of raw or undercooked meats, or by faecal contamination of foodstuffs or water supplies.
How does this affect drinking water?
Because E.coli are always present in human and animal faeces in very high numbers, they are used as an indicator of faecal pollution in the microbiological surveillance of drinking water. On very rare occasions, low numbers of E.coli are detected in drinking water. This does not indicate that O157 is present, or that there is an immediate risk to health. Detection of E.coli does however necessitate an immediate investigation of the water supply system in order to identify and eliminate the source of pollution.
How is E coli dealt with?
All E.coli bacteria are rapidly inactivated by chlorine and other disinfectants used in the treatment of public water supplies. Drinking water related cases of infection are invariably associated with unchlorinated supplies or with systems where there is poor maintenance or operation of disinfection systems. In the UK, no O157 infections have been associated with public water supplies. Some cases have occurred where consumers use private water supplies that are not disinfected.
